Researchers report that many neurons in the fetal brain have large DNA abnormalities, but the share drops sharply around birth, suggesting the developing brain selectively removes some cells with genetic problems.
In a study published Oct. 28 in Nature, scientists used single-cell sequencing to examine 2,357 individual neurons from human brain tissue from fetal life through after birth, looking for copy number variants, or sections of DNA that were duplicated or missing. On average, about 26% of neurons in the cortex before birth had widespread variants, compared with roughly 6% of neurons after birth. The researchers also examined tens of thousands of additional cell nuclei and found a similar pattern, strengthening the evidence that the change is real.
Neurons with more DNA abnormalities showed unusual activity in genes involved in making and maintaining synapses, the connections through which neurons communicate. The results suggest these cells may be less able to join neural circuits. They could also be more likely to die during the normal period of cell elimination around birth.
The study did not follow individual cells over time. The decline therefore supports, but does not directly prove, that abnormal neurons are selectively removed. The findings raise the question of whether problems with this apparent process for removing faulty cells could contribute to neurodevelopmental conditions.
They do not establish that the process causes autism or other disorders.